The invention is in the field of processing waveforms, particularly waveforms representing pulses such as may be detected by radar warning receivers, or electronic warfare countermeasures equipment.
In prior art systems, it is well known to use a Detector Log Video Amplifier (DLVA) to detect microwave signals varying in amplitude by up to 80 decibels. Generally the signals being detected are in the form of pulses. The DLVA is able to process signals of such a wide dynamic range because it has a logarithmic, or compressive, transfer response rather than a linear response. The gain of the amplifier in this case is dependent on input power level, and a signal of small amplitude will be amplified to a greater degree than a signal of large amplitude. One problem encountered in such prior art systems is that if a short pulse of small amplitude is incident on a longer pulse of large amplitude, the small pulse will be processed along with the large pulse, and therefore will be compressed to a greater degree than if the large pulse had not been present.
In prior art systems, important information can be obscured or lost when a signal from more than one source is being detected. The Compression Video Amplifier (CVA) processes the small pulse as if it were merely a perturbation on the larger pulse. Therefore, the small pulse is actually seen as a pulse of nearly equal magnitude to the larger pulse. In fact, previously it was often impossible to determine whether the small pulse even was a pulse, within the error limits of the CVA.
In particular, suppose that the CVA output is accurate to within +/-0.5 dB. Furthermore, suppose a pulse of magnitude -10 dBm is superimposed on a pulse of magnitude 0 dBm. The composite pulse would be 0.4 dBm. Accuracy within +/-0.5 dB at this level is equivalent to +/-0.12 milliwatts, which translates to over 3 dB when referenced back to the smaller pulse. Naturally, this error is compounded when pulses are considered which are further apart in dynamic range. However, when the original waveform is fed into a circuit embodying the present invention, pulse magnitude fidelity can be preserved.
Prior art systems are known which utilize an AC-Coupled DLVA in order to enhance a small pulse which is present on a CW signal (which might be considered an infinitely long, large pulse). However, it is believed that the present invention is the first system in which a small pulse can be accurately extracted from a larger pulse of finite length.